Discotic compounds for use in liquid crystal mixtures

ABSTRACT

Liquid crystal compounds have been synthesized of general formula (I) and may be mixed with other liquid crystal compounds to give useful liquid crystal mixtures which may then be used in liquid crystal devices. Such devices include linear and non-linear electrical, optical and electro-optical devices, magneto-optical devices and devices providing responses to stimuli such as temperature changes and total or partial pressure changes. Formula (I) where each Z 1-6  is given by formula (II), where Y for each of Z 1-6  is independently COO, OCO, CH 2  O and OCH 2 , m defines the number of substituents on each of Z 1-6  and is independently 0-5,and X is independently for each substituent on each of Z 1-6  alkyl (straight chain, branched and chiral), alkoxy (straight chain, branched or chiral), alkanoyl (straight chain, branched or chiral), alkenyl (straight chain, branched or chiral), halogen, halogenoalkyl (straight chain, branched or chiral) and CN, provided that at least one of Z -6  1 has at least one substituent X, and excluding where m is 1 for each of Z 1-6 , Y is COO for each of Z 1-6  and X is n-alkyl or n-alkoxy positioned para to Y for each of Z 1-6  and also where M is 5 for each of Z 1-6 , Y is COO for each of Z 1-6  and for each Z 1-6  X is selected as n-alkoxy positioned para to Y and fluoride for all other substituents.

This is a national phase filing of PCT/GB93/01291 having aninternational filing date of Jun. 16, 1993, published as WO94/29263 Dec.22, 1994.

BACKGROUND OF THE INVENTION

This invention relates to discotic compounds and to their use in liquidcrystalline materials and liquid crystal devices.

The majority of known liquid crystalline compounds have a generallyrod-shaped molecular structure, and are often characterised by nematicand/or smectic mesophases. However, there are a number of knowncompounds which are characterised by a generally disc-like molecularstructure. These compounds are termed discotic compounds, which can becharacterised by anisotropic mesophase(s).

Discotic compounds can be based on a number of "cores", eg benzene,truxene, metallophthalocyanine and triphenylene described in SChandrasekhar and G S Ranganath in Rep Prog Phys 53 (1990) pp 57-84.Nguyen Huu Tinh et al (Mol. Cryst. Liq. Cryst., (1981), Vol 68, pp101-111) describe 2,3, 6,7, 10,11 triphenylene n-alkoxy (and n-alkyl)esters. C Vauchier et al (Mol. Cryst. Liq Cryst., Vol 66 (1981) pp103-114) have also described 2,3, 6,7, 10,11 n-alkoxy benzoates andn-alkoxy tetra-fluoro substituted benzoates of triphenylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a synthetic route for preparing the compound of Example 1.

FIG. 2 is a synthetic route for preparing the compound of Example 2;

FIG. 3 is a synthetic route for preparing the compound of Example 3;

FIG. 4 is a synthetic route for preparing the compound of Example 4;

FIG. 5 is a synthetic route for preparing the compound of Example 5;

FIG. 6 is a synthetic route for preparing the compound of Example 6;

FIG. 7 is a synthetic route for preparing the compound of Example 7;

FIG. 8 is a phase diagram illustrating weight percent of a mixture oftwo compounds versus temperature;

FIG. 9 is a phase diagram illustrating weight percent of compound versustemperature for selected compounds of pairs of compounds;

FIG. 10 is a phase diagram illustrating weight percent of compoundversus temperature for selected compounds of pairs of compounds;

FIG. 11 is a phase diagram illustrating weight percent of compoundversus temperature for selected compounds of pairs of compounds; and

FIG. 12 is a phase diagram illustrating weight percent of compoundversus temperature for selected compounds of pairs of compounds;

FIG. 13 is a schematic cross-section of a liquid crystal display devicecontaining the liquid crystal materials of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to this invention 2,3,6,7,10,11 triphenylene discoticcompounds are provided of Formula I: ##STR2## where each of Z₁₋₆ isgiven by Formula II: ##STR3## where Y for each of Z₁₋₆ is independentlyselected from COO, OCO, CH₂ O, and OCH₂, m defines the number ofsubstituents on each of Z₁₋₆ and is independently selected from 0-5, andX is independently selected for each substituent on each of Z₁₋₆ fromalkyl (straight chain, branched and chiral), alkoxy (straight chain,branched or chiral), alkanoyl (straight chain, branched or chiral),alkenyl (straight chain, branched or chiral), halogen, halogenoalkyl(straight chain, branched or chiral) and CN, provided that at least oneof Z₁₋₆ has at least one substituent X, and excluding where m is 1 foreach of Z₁₋₆, Y is COO for each of Z₁₋₆ and X is n-alkyl or n-alkoxypositioned para to Y for each of Z₁₋₆, and also where m is 5 for each ofZ₁₋₆, Y is COO for each of Z₁₋₆ and for each Z₁₋₆ X is selected asn-alkoxy positioned para to Y and fluorine for all other substituents.

Where substituent(s) are selected from alkyl, alkoxy, or alkenyl, thensuch substituents are preferably selected from C₁₋₂₀.

The structural preferences discussed below are inter alia on the basisof ease of preparation and/or usefulness in liquid crystal materials.

Preferred structures for each of independently selected Z₁₋₆ are givenbelow: ##STR4## where X_(j) is selected from alkyl, alkoxy, halogen(preferably fluorine) and CN.

Typically compounds of Formula I can be prepared by reaction of theappropriately substituted benzoic acid with the appropriate triphenylenebiphenol. Preparation of triphenylene phenols is known (eg N H Tinh etal Mol. Cryst. Liq. Cryst., (1981), Vol 68, pp 101-111). Theappropriately substituted benzoic acid can be prepared from syntheticroutes apparent to persons skilled in the art.

In another aspect of this invention, compound(s) of Formula I can beincluded in a mixture, where the mixture comprises at least twocompounds. Typical mixtures include mixtures consisting of compounds ofFormula I, and also mixtures comprising at least one compound of FormulaI and at least one compound not of Formula I. Donor/acceptor mixtures,and mixtures having lower melting points than melting points ofindividual compounds, are desirable for obtaining room temperatureliquid crystal phases in discotic liquid crystal materials and forcontrol of phase sequence and transition temperatures.

A further aspect of the invention includes use of the compounds ofFormula I, and use of mixtures including Formula I, in a liquid crystaldevice. Typically such devices include linear and non-linear electrical,optical and electro-optical devices, magneto-optical devices, anddevices providing responses to stimuli such as temperature changes andtotal or partial pressure changes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described by way of example only, in whichFIGS. 1-7 describe synthetic routes for the preparation of examplecompounds 1-7. FIGS. 8-12 are phase diagrams illustrating wt % ofcompound versus temperature. FIG. 13 illustrates a liquid crystaldevice.

Compound 1. Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-3-methylbenzoate.

Step 1.1 Preparation of hexamethoxytriphenylene.

Chloranil (64 g, 0.26 mol), veratrol (14.4 g, 0.104 mol) and dilutesulphuric acid (70% v/v, 200 ml) were added together under nitrogen withstirring. The reaction was left for 8 days. The contents of the flaskwere poured onto ice (1 liter) and further diluted in 3 liters of water.The solid was filtered off. The product was first resuspended in 1 literof water and 100 ml methanol and filtered off. This procedure wasrepeated using 500 ml methanol and 50 ml of water and finally with 1liter of methanol. The product was then filtered off and dried. Thematerial was then taken up into chloroform and filtered, this procedurewas repeated several times. The combined chloroform extracts wereevaporated and the solid stirred with 3×100 ml of toluene, filtered offand air dried. Then the solid was stirred with 3×100 ml of acetone,filtered off and air dried. The crude product was suspended in 100 mlchloroform together with 20 g of silica (Merck 60H, ART 7736). Thisslurry was added to a column of silica (60H, 80 g) in a 1 litercylindrical separating funnel and eluted with chloroform. The fractionscollected were stirred with an equal volume of toluene +3×that volume ofmethanol. The precipitated hexamethoxytriphenylene was then filteredoff.

Yield: 3.26 g, (23%),

Melting point: 315° C.

Step 1.2 Preparation of hexahydroxytriphenylene.

Boron tribromide (8.6 g, 0.034 mol) in dry dichloromethane (80 ml) wasadded to hexamethoxytriphenylene (2 g, 0.0049 mol) in drydichloromethane (100 ml) under a dry nitrogen atmosphere at -80° C. Themixture was allowed to warm to room temperature overnight. Water wasadded and the dichloromethane was removed under reduced pressure. Thecrude product was filtered off. The hexahydroxytriphenylene was purifiedby recrystallisation from water.

Yield: 1 g, (63%),

Melting Point: >310° C.

Step 1.3 Preparation of 2-methylphenyl acetate.

Ice (300 g) was added to o-cresol (21.6 g, 0.2 mol) dissolved in asolution of sodium hydroxide (12 g, 0.3 mol in water (100 ml). Aceticanhydride (30.6 g, 0.3 mol) was then added and the mixture was shakenfor 1 min. The product was extracted into ether and then purified byreduced pressure distillation.

Yield: 25 g, (83.3%),

Boiling point: 66° C., 1 mmHg.

Step 1.4 Preparation of 4-hydroxy-3-methylacetophenone.

Compound of step 1.3 (24.7 g, 0.16 mol) in dry nitrobenzene (125 ml) wasadded dropwise with stirring to a suspension of anhydrous aluminiumchloride (42.6 g, 0.32 mol) in dry nitrobenzene (250 ml) cooled in ice.The mixture was allowed to warm to room temperature and the stirring wascontinued for 10 hrs. The mixture was then poured onto ice andconcentrated hydrochloric acid (100 ml) and stirred for 0.5 hrs. Theorganic layer was separated, and the aqueous layer was shaken withchloroform. The combined organic layers were washed with brine and thensteam distilled until no further solvent (chloroform and nitrobenzene)passed over. The resultant crude product was extracted into chloroformand dried over anhydrous magnesium sulphate. After the chloroform wasremoved, the methyl-ketone was purified by recrystallisation from a 1:1mixture of ethyl acetate and petroleum fraction (b.p. 60°-80° C.).

Yield: 5.36 g, (22%).

Melting point: 107°-109° C.

Step 1.5 Preparation of 3-methyl-4-octyloxyacetophenone.

Compound of step 1.4 (5 g, 0.033 mol) was added with stirring to asuspension of potassium carbonate (22.77 g, 0.165 mol) in butanone (110ml). Bromo-octane (6.76 g, 0.035 mol) was then added dropwise. Themixture was stirred under reflux for 24 hrs. The solid was filtered offand half of the solvent was removed. The solution was then poured intowater and the product was extracted into ethyl acetate. The combinedextracts were washed with aqueous sodium hydroxide (5%) and then withwater. After drying the extract over anhydrous magnesium sulphate. Themethyl-ketone was purified by reduced pressure distillation.

Yield: 5.58 g, (64%),

Boiling point: 174° C., 1 mmHg.

Step 1.6 Preparation of 3-methyl-4-octyloxybenzoic acid.

A solution of sodium hypobromite was prepared at -10°-0° C. bydissolving bromine (12.8 g, 0.08 mol) in a solution of sodium hydroxide(8 g, 0.2 mol) in water (38 ml). This solution was added with stirringto a solution of compound of step 1.5 (3 g, 0.0115 mol) in dioxan (125ml). The temperature was maintained at 60°-70° C. throughout theaddition and for a further 20 mins. The excess of hypobromite wasdestroyed with sodium metabisulphite. Water was added to the reactionmixture, the white precipitate was filtered off and then the solutionwas acidified with concentrated hydrochloric acid. The precipitate wasfiltered off, washed several times with water, and then dried overanhydrous magnesium sulphate. The acid was purified by recrystallisationfrom ethanol.

Yield: 1.42 g, (46%),

Transitions (°C.): K₁ 70.9 K₂ 112.4 (N 102.4) IL.

Step 1.7 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-3-methylbenzoate.

Compound of step 1.6 (10 g, 0.038 mol) and Dimethylformamide (5 drops)were dissolved in dry dichloromethane (100 ml) and oxalyl chloride (9.6g, 0.076 mol) in dry dichloromethane (10 ml) was added dropwise. Themixture was stirred at room temperature overnight. The excess of oxalylchloride and dichloromethane was removed in vacuo (60° C.) and theresidual acid chloride was then used at once to prepare the ester.3-methyl-4-octyloxybenzoyl chloride (0.038 mol) was added to thecompound of step 1.2 (0.6 g, 0.0019 mol) in anhydrous pyridine (100 ml).The mixture was heated with stirring at 160° C. for 2 hrs and thenpoured onto a mixture of concentrated hydrochloric acid (50 ml) andcrushed ice (500 ml). The crude product was extracted into ether, washedwith water, and dried over anhydrous magnesium sulphate. The solvent wasremoved and the product was purified by flash column chromatography(dichloromethane eluent) and successive recrystallisations from ethanol.

Yield: 0.8 g, (23%),

Transitions (°C.): K 50 N_(D) 208 IL.

Compound 2. Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-3-fluorobenzoate.

Step 2.1 Preparation of 4-Bromo-1-decyloxy-2-fluorobenzene.

A solution of 1-bromodecane in butanone was added dropwise to a stirredrefluxing solution of 4-bromo-2-fluorophenol and potasium carbonate. Thestirred mixture was heated under reflux for 24 hr. The potassiumcarbonate was filtered off and the solvent removed. The product wasdistilled at 130° C. at 0.05 mmHg.

Step 2.2 Preparation of 4-decyloxy-3-fluorobenzoic acid.

A solution of n-butyllithium was added dropwise to a stirred, cooled(-78° C.) solution of compound of step 2.1 in dry THF. The mixture wasmaintained under these conditions for 40 mins and then poured into aslurry of dry ether and cardice. The solution was acidified with 36%HCl, washed with water and dried (magnesium sulphate). The solvent wasremoved to yield a white solid.

K 103.5 S_(c) 109.6N 114.7 I

Step 2.3 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-3-fluorobenzoate.

Compound of step 2.2 and dimethylformamide were dissolved in drydichloromethane. A solution of oxalyl chloride in dry dichloromethanewas added dropwise. The reaction was left overnight and then solvent andexcess oxalyl chloride was removed. The residual acid chloride was usedimmediately. Compound of step 1.2 was added to the acid chloride in drypyridine at 160° C. and heated under reflux for 2 hours. The reactionwas cooled and poured into a mixture of 36% HCl/ice. The crude productwas extracted into ether, washed with water, sodium bicarbonate, waterand dried (magnesium sulphate). The solvent was removed to yield a crudeproduct, which was recrystallised in benzene.

K 175 M₁ 216 M₂ about 320 M₃ about 430 I (decomposes) where M₁₋₃ areconsidered to be unknown mesophases.

Compound 3. Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2,6-dimethyl benzoate.

Step 3.1, Preparation of 1-Bromo-4-decyloxy-2,6-dimethylbenzene.

The experimental procedure was as described for the preparation of thecompound formed by step 2.1

A solution of 1-bromodecane (11.05 g, 0.05 mol) in butanone (50 ml) wasadded dropwise to a stirred, refluxing mixture of4-Bromo-3,5-dimethylphenol (8.0 g, 0.04 mol) and anhydrous potassiumcarbonate K₂ CO₃ (30.0 g, 0.2 mol) in butanone (250 ml). The stirredmixture was heated under reflux for 24 h. The K₂ CO₃ was filtered offand the solvent removed. The residue was distilled to yield a colourlessliquid.

Step 3.2, Preparation of 4-Decyloxy-2,6-dimethylbenzoic acid

The experimental procedure was as described for the preparation of thecompound formed by step 2.2

A solution of n-butyllithium (2.9 ml, 10.0M in hexane, 0.029 mol) wasadded dropwise to a stirred, cooled (-78° C.) solution of1-Bromo-4-decyloxy-2,6-dimethylbenzene (10.0 g, 0.029 mol) in dry THF(200 ml) under dry nitrogen. The stirred mixture was maintained underthese conditions for 1 h and then poured onto a slurry of solid carbondioxide and dry ether. The product was acidified with 36% HCl and washedwith water. The ether layer was dried (MgSO₄) and the solvent removed togive a colourless solid which was recrystallised from petroleum fraction(40°-60° C.).

Yield: 2.64 g (30%)

mp=80°-81° C.

Step 3.3 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2,6-dimethyl benzoate.

A solution of oxalyl chloride (1.26 g, 0.01 mol) in dry dichloromethanewas added dropwise to a stirred solution of4-Decyloxy-2,6-dimethylbenzoic acid (2.44 g, 0.008 mol) and DMF (10drops) in dry dichloromethane (100 ml). The reaction was left overnightand then the solvent was removed. The residual acid chloride was usedimmediately without further purification.

2,3,6,7,10,11-Hexahydroxytriphenylene (0.26 g, 0.0085 mol) was added allat once to the acid chloride in dry pyridine and was heated under reflux(oilbath temperature at >160° C.) for 2 h. The reaction mixture wascooled and poured into a mixture of concentrated hydrochloric acid andice. The crude product was extracted into ether, washed with water,aqueous NaHCO₃, water and dried (MgSO₄). The solvent was removed, thecrude product was purified by flash column chromatography andrecrystallised from ethanol/ethyl acetate.

Yield: 2.68 g (58%)

Compound 4: Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-3,5-dimethyl benzoate.

Step 4.1 Preparation of 1-Bromo-4-decyloxy-3,5-dimethylbenzene.

The experimental procedure was as described for the preparation of1-Bromo-4-decyloxy-2,6-dimethylbenzene (see step 3.1) and the productwas distilled.

Quantities: 4-Bromo-2,6-dimethylphenol (8.0 g, 0.04 mol), 1-bromodecane(11.05 g, 0.05 mol), K₂ CO₃ (30.0 g, 0.2 mol).

Yield: 12.0 g, (88%),

bp=150°-160° C. at 0.01 mm Hg.

Step 4.2, Preparation of 4-Decyloxy-3,5-dimethylbenzoic acid

The experimental procedure was as described for the preparation of4-Decyloxy-2,6-dimethylbenzoic acid (see step 3.2). The product wasrecrystallised from petroleum fraction (40°-60° C.).

Quantities: 1-Bromo-4-decyloxy-3,5-dimethylbenzene (12.0 g, 0.039 mol),n-butyllithium (3.9 ml, 10.0M in hexane. 0.039 mol).

Yield: 4.44 g, (37%)

mp=77°-78° C.

Step 4.3: Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-3,5-dimethyl benzoate.

The experimental procedure was as described for the preparation ofTriphenylen-2,3,6,7,10,11-yl hexa-4-decyloxy-2,6-dimethyl benzoate (seestep 3.3).

Quantities: 1-Bromo-4-decyloxy-3,5-dimethylbenzene (4.0 g, 0.013 mol),oxalyl chloride (3.78 g, 0.03 mol),2,3,6,7,10,11-Hexahydroxytriphenylene (0.42 g, 0.0013 mol).

Yield: 0.28 g (11%)

Compound 5: Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2,6-difluorobenzoate.

This compound was synthesised in a similar manner as that described forcompound 2.

Step 5.1 Preparation of 1-Decyloxy-3,5-difluorobenzene.

The experimental procedure was as described for the preparation of1-Bromo-4-decyloxy-3-fluorobenzene (see step 2.1).

Quantities: 3,5-difluorophenol (5.0 g, 0.038 mol), 1-bromodecane (8.84g, 0.04 mol).

Yield: 10.26 g (100%)

Step 5.2 Preparation of 4-Decyloxy-2,6-difluorobenzoic acid

The experimental procedure was as described for the preparation of4-decyloxy-3-fluorobenzoic acid (see step 2.2).

Quantities: 1-Decyloxy-3,5-difluorobenzene (10.26 g, 0.038 mol), n-BuLi(10.0M), (3.8 ml, 0.038 mol), THF (200 ml).

Yield: 7.7 g, (64%).

Step 5.3 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2,6-difluorobenzoate.

The experimental procedure was as described for the preparation oftriphenylen-2,3,6,7,10,11-yl hexa-4-decyloxy-3-fluorobenzoate (see step2.3).

Quantities: 4-Decyloxy-2,6-difluorobenzoic acid (7.7 g, 0.024 mol),oxalyl chloride (3.78 g, 0.03 mol), DMF (10 drops), dichloromethane (100ml), hexahydroxytriphenylene (0.77 g, 0.0024 mol), pyridine (100 ml).

Yield: 3.00 g (60%)

Phase Transition/°C.: K 138.0 I

Compound 6: Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-3-decyloxybenzoate.

This compound was synthesised in a similar manner as that described forcompound 2.

Step 6.1 Preparation of Methyl 3-hydroxybenzoate.

3-hydroxybenzoic acid (30.0 g, 0.22 mol), methanol (101 ml) andconcentrated sulphuric acid (2.7 ml) were added together and heatedunder reflux for 4 h. The reaction mixture was allowed to cool and themethanol was removed. The crude product was dried in vacuo and usedwithout further purification.

Yield: 32.98 g, (100%).

Step 6.2 Preparation of Methyl 3-decyloxybenzoate.

A solution of 1-bromodecane (11.05 g, 0.050 mol) in butanone (50 ml) wasadded dropwise to a stirred, refluxing mixture ofmethyl-3-hydroxybenzoate (5.0 g, 0.033 mol) and anhydrous potassiumcarbonate (K₂ CO₃) (30.0 g, 0.20 mol) in butanone (200 ml). The stirredmixture was heated under reflux for 24 h. The K₂ CO₃ was filtered offand the solvent removed. The residue was purified by gravity columnchromatography (silica gel/dichloromethane) to yield a colourless oil.

Yield: 9.64 g, (100%).

Step 6.3 Preparation of 3-Decyloxybenzoic acid.

A solution of methyl 3-decyloxybenzoate (9.64 g, 0.033 mol) and sodiumhydroxide (6.60 g, 0.165 mol) in methanol (150 ml) and water (15 ml) washeated under reflux for 2 h. The reaction mixture was then allowed tocool, followed by addition of dilute HCl (100 ml). The crude product wasfiltered off, washed with water and then dried in vacuo. The materialwas recrystallised to yield colourless crystals.

Yield: 7.60 g, (82%).

Step 6.4 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-3-decyloxybenzoate.

The method of preparation of this compound was the same as for step 3.3

Yield: 4.83 g (95%)

Phase Transition/°C.: K 134.0 I

Compound 7: Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2-ethyl-6-methylbenzoate.

Step 7.1 Preparation of 1-Decyloxy-3-ethyl-5-methylbenzene.

The experimental procedure was as described for1-Bromo-4-decyloxy-3-fluorobenzene (see step 2.1) to yield a pale orangeoil.

Quantities: 3-ethyl-5-methylphenol (5.0 g, 0.036 mol), 1-bromodecane(11.05 g, 0.05 mol), K₂ CO₃ (30.0 g, 0.2 mol).

Yield: 9.4 g (94%).

Step 7.2 Preparation of 1-Bromo-4-decyloxy-2-ethyl-6-methylbenzene

A solution of bromine (5.44 g, 0.034 mol) in chloroform (50 ml) wasadded dropwise to a stirred, refluxing solution of1-decyloxy-3-ethyl-5-methylbenzene (9.4 g, 0.034 mol) in chloroform (200ml). The reaction mixture was then allowed to cool, washed with waterand dried (MgSO₄). The solvent was removed and the residue purified bygravity column chromatography (silica gel/dichloromethane) to yield apale orange oil.

Yield: 11.57 g (96%).

Step 7.3 Preparation of 4-Decyloxy-2-ethyl-6-methylbenzoic acid

The experimental procedure was as described for the preparation of thecompound synthesised in step 2.2. The crude product was recrystallisedfrom petroleum fraction (40°-60° C.) to yield a colourless solid.

Quantities: 1-bromo-4-decyloxy-2-ethyl-6-methylbenzene (11.57 g, 0.036mol), n-BuLi (3.6 ml, 10.0M, 0.036 mol), THF (200 ml).

Yield: 4.32 g (48%).

Step 7.4 Preparation of Triphenylen-2,3,6,7,10,11-ylhexa-4-decyloxy-2-ethyl-6-methylbenzoate.

The experimental procedure was as described for compound 2, (see step2.3).

Quantities: 4-decyloxy-2-ethyl-6-methylbenzoic acid (4.32 g, 0.0135mol), oxalyl chloride (1.89 g, 0.015 mol), DMF (10 drops),dichloromethane (100 ml), hexahydroxytriphenylene (0.44 g, 0.00135 mol),pyridine (100 ml).

Yield: 1.15 g (40%).

Phase Transition: K-N_(D) 70.0 I

Tables 1 and 2 give phase transition temperatures for compounds ofFormula I, where Formula III describes each of Z₁₋₆ for Table 1, FormulaIV describes each of Z₁₋₆ for Table 2, and K is crystalline, D is acolumnar phase, N_(D) is nematic discotic phase and IL is isotropicliquid. Formula V describes each of Z₁₋₆ for Table 3, Formula VIdescribes each of Z₁₋₆ for Table 4. K is crystalline. D is a columnarphase, N_(D) is nematic discotic phase, hd is hexagonal disordered andIL is isotropic liquid. ##STR5##

All phase transition temperatures were obtained by microscopy, unlessdescribed within brackets. Data within brackets indicates that phasetransition temperatures were obtained using a differential scanningcalorimeter.

                  TABLE 1                                                         ______________________________________                                        n            Phase Transition Temperatures (°C.)                       ______________________________________                                        6            K 185 N.sub.D 242 IL                                                          (K 59 D 110 N.sub.D 242 IL)                                      7            K 152 N.sub.D 215 IL                                                          (K 30 D 138 N.sub.D 209 IL)                                      8            K 50 N.sub.D 208 IL                                                           (K 37 D 123 N.sub.D 205 IL)                                      9            K 114 N.sub.D 202 IL                                                          (K 40 D 113 N.sub.D 201 IL)                                      10           K 77 N.sub.D 180 IL                                                           (K 40 D 94 N.sub.D 178 IL)                                       11           K 92 N.sub.D 165 IL                                                           (K 92 N.sub.D 154 IL)                                            12           K 126 N.sub.D 166 IL                                                          (K 44 D 90 N.sub.D 163 IL)                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        n            Phase Transition Temperatures (°C.)                       ______________________________________                                        7            K 145 N.sub.D 208 IL                                                          (K 32 D 139 N.sub.D 201 IL)                                      8            K 127 N.sub.D 199 IL                                                          (K 67 D 123 N.sub.D 195 IL)                                      9            K 114 N.sub.D 179 IL                                                          (K 45 D 108 N.sub.D 174 IL)                                      10           K 109 N.sub.D 180 IL                                                          (K 40 N.sub.D 164 IL)                                            11           K 106 N.sub.D 136 IL                                                          (K 103 N.sub.D 134 IL)                                           12           K 105 N.sub.D 115 IL                                                          (K 97 N.sub.D 141 IL)                                            ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                    Phase                                                                         Transitions/°C.                                            R              K         N.sub.D   I                                          ______________________________________                                        C.sub.6 H.sub.13                                                                             * 170     * 196     *                                          C.sub.8 H.sub.17                                                                             * 155     * 170     *                                          C.sub.10 H.sub.21                                                                            * 108     * 134     *                                          C.sub.12 H.sub.25                                                                            * 88      * 99      *                                          C.sub.6 H.sub.13 CH(CH.sub.3)                                                                * 161     * --      *                                          ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                     Phase                                                                         Transitions/°C.                                           R            K        D.sub.hd N.sub.D                                                                              I                                       ______________________________________                                        C.sub.6 H.sub.13 ¶                                                               * 150    * 210    * 243  *                                       C.sub.8 H.sub.17                                                                           * 170    * 195    * 215  *                                       C.sub.10 H.sub.21                                                                          * 157    * 167    * 182  *                                       C.sub.12 H.sub.25                                                                          *        * 143    * 151  *                                       C.sub.6 H.sub.13 CH(CH.sub.3)                                                              * 125    * 156    * 183  *                                       ______________________________________                                         ¶ DSC data; material decomposes under microscopic examination  

The compounds of formula I may be added to other materials to formmixtures. FIG. 8 is a phase diagram showing the weight % of: ##STR6##when mixed with the compound illustrated below versus transitiontemperature. ##STR7##

FIG. 9 is a binary phase diagram of transition temperatures plottedagainst % by weight for compounds triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxybenzoate and triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-3,5-dimethylbenzoate.

FIG. 10 is a binary phase diagram of transition temperatures plottedagainst % by weight for compounds triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-3,5-dimethylbenzoate and triphenylen-2,3,6,7,10,11-ylhexa-4-dodecyloxy-3,5-dimethylbenzoate.

FIG. 11 is a binary phase diagram of transition temperatures plottedagainst % by weight for compounds triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-2,6-dimethylbenzoate and triphenylen-2,3,6,7,10,11-ylhexa-4-dodecyloxy-2,6-dimethylbenzoate.

FIG. 12 is a binary phase diagram of transition temperatures plottedagainst % by weight for compounds triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-3,5-dimethylbenzoate and triphenylen-2,3,6,7,10,11-ylhexa-4-octyloxy-2,6-dimethylbenzoate.

An example of the use of a compound of Formula I in a liquid crystalmaterial and device embodying the present invention will now bedescribed with reference to FIG. 13.

The liquid crystal device consists of two transparent plates, 1 and 2,in this case made from glass. These plates are coated on their internalface with transparent conducting electrodes 3 and 4. An alignment layer5, 6 is introduced onto the internal faces of the cell so that a planarorientation of the molecules making up the liquid crystalline materialwill be approximately parallel or at a small angle to the glass plates 1and 2. For some types of display the alignment directions areorthogonal. The electrodes 3, 4 may be formed into row and columnelectrodes so that the intersections between each column and row form anx, y matrix of addressable elements or pixels. A spacer 7 eg ofpolymethyl methacrylate separates the glass plates 1 and 2 to a suitabledistance eg 2 microns.

Liquid crystal material 8 is introduced between glass plates 1, 2 byfilling the space in between them. The spacer 7 is sealed with anadhesive 9 in a vacuum using an existing technique. Polarisers 10, 11are arranged in front of and behind the cell. For some devices, only oneor even no polarisers are required.

The device may operate in a transmissive or reflective mode. In theformer, light passing through the device, eg from a tungsten bulb, isselectively transmitted or blocked to form the desired display. In thereflective mode a mirror (12) is placed behind the second polariser 11to reflect ambient light back through the cell and two polarisers. Bymaking the mirror partly reflecting the device may be operated both in atransmissive and reflective mode.

In another example a layer of liquid crystal material is exposed to agas to provide a gas sensor.

We claim:
 1. A 2,3,6,7,10,11 triphenylene discotic compound of FormulaI: ##STR8## where each of Z₁₋₆ is given by Formula II: ##STR9## where Yfor each of Z₁₋₆ is independently selected from the group consisting ofCOO and OCO, m defines the number of substituents on each of Z₁₋₆ and isindependently selected from the group consisting of 1-5, and X isindependently on each of Z₁₋₆ selected from the group consisting of astraight chain, branched and chiral alkyl a straight chain, branched orchiral alkoxy, a straight chain, branched or chiral alkanoyl, a straightchain, branched or chiral alkenyl, halogen, a straight chain, branchedor chiral halogenoalkyl and CN, provided that at least one of Z₁₋₆ hasat least one substituent X which is in the ortho or meta positionrelative to the Y group excluding where m is 5 for each Z₁₋₆, Y is COOfor each of Z₁₋₆ and for each Z₁₋₆ X is as n-alkoxy positioned para to Yand fluorine for all other substituents.
 2. A triphenylene according toclaim 1 wherein each of Z₁₋₆ is the same.
 3. A triphenylene according toclaim 1 where Y is COO for each of Z₁₋₆.
 4. A triphenylene according toclaim 3 where each Z₁₋₆ has a substituent positioned para with respectto Y, and the substituent for each of Z₁₋₆ is selected from the groupconsisting of alkyl, alkoxy, fluorine, chlorine and CN.
 5. Atriphenylene according to claim 4 where at least one Z₁₋₆ in the orthoor meta substituent portions is selected from the group consisting ofCH₃, fluorine, chlorine and CF₃.
 6. A triphenylene according to claim 4where at least one Z₁₋₆ has three substituents, two of the substituentsare selected from the group consisting of CH₃, fluorine, chlorine andCF₃, and are positioned ortho and meta with respect to Y.
 7. Atriphenylene according to claim 4 where at least one Z₁₋₆ has threesubstituents, two of the substituents are selected from the groupconsisting of CH₃, fluorine, chlorine and CF₃, and both are positionedmeta with respect to Y.
 8. A liquid crystal mixture, comprising at leasttwo compounds, where at least one compound is a triphenylene accordingto claim
 1. 9. A liquid crystal mixture, comprising at least twocompounds, where all compounds in the mixture are triphenylenesaccording to claim
 1. 10. A liquid crystal device incorporating atriphenylene according to claim 1.